Setting wayland environment variables at startup

[nova-nowiz]

Describe your PR, what does it fix/add?

Answers different issues brought up in #850

• sets XDG_BACKEND and _JAVA_AWT_WM_NONREPARENTING to wayland and 1 at startup, so that the user doesn't have to worry setting these up.
• removed these variables from nix modules recommended environment
• removed XCURSOR_SIZE from nix modules as it is already set

Is there anything you want to mention? (unchecked code, possible bugs, found problems, breaking compatibility, etc.)

NIXOS_OZONE_WL for now stays in the nix modules as it would clutter non-nixos users environment variables and doesn't seem to interact badly with x11 sessions, though it it possible that it could.

Is it ready for merging, or does it need work?

it is fully ready to be merged

@fufexan

[vaxerski]

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[nova-nowiz]

forgot to ping @viperML.

[nova-nowiz]

Thanks!